Digital camera

ABSTRACT

A digital camera includes a shutter button. When taking a still picture of a subject in response to operation of the shutter button, a TG carries out first exposure and second exposure. The first exposure and the second exposure are simultaneously started by the suspension of outputting a charge sweep-out pulse. Elapsing a first exposure period, the TG reads a first charge out of a part of the light-receiving elements, thereby ending the first exposure. Elapsing a second exposure period, a mechanical shutter is closed thereby ending the second exposure. A second charge produced due to the second exposure is read out after completing the transfer of the first charge. The first and second charges outputted from the CCD imager are combined together by an image combining circuit.

BACKGROUND OF THE INVENTION

[0001] 1.Field of the Invention

[0002] This invention relates generally to digital cameras and, moreparticularly, to a digital camera which generates a still image signalof one screen on the basis of the first charge produced due to firstexposure by the image sensor and the second charge produced due tosecond exposure by the image sensor.

[0003] 2.Description of the Prior Art

[0004] There is an example of a conventional digital camera of this kindas disclosed in Japanese Patent Laid-open No. 75118-1999[H04N5/335,H04N5/232] laid open on Mar. 16, 1999. This prior art aims at generatinga still image signal extended in dynamic range by combining the chargeacquired by long-time exposure and the charge due to short-timeexposure. In the prior art, however, the short-time exposure is carriedout after the completion of the long-time exposure. This increases thetotal time needed for exposure, thus resulting in a blurred picturetaken of a subject moving at high speed.

SUMMARY OF THE INVENTION

[0005] Therefore, it is a primary object to provide a digital cameracapable of preventing against a blurred picture taken of a subject.

[0006] A digital camera according to the present invention comprises: animage sensor formed, in a light-receiving surface, with a plurality offirst light-receiving elements and a plurality of second light-receivingelements; a first exposer for subjecting the first light-receivingelements to first exposure for a first period; a second exposer forsubjecting the second light-receiving elements to second exposure for asecond period; an outputter for separately outputting, from the imagesensor, a first charge produced in the first light-receiving elementsdue to the first exposure and a second charge produced in the secondlight-receiving elements due to the second exposure; and a generator forgenerating a still image signal of one screen on the basis of the firstcharge and the second charge; wherein the first period is shorter thanthe second period and overlapped in time with the second period.

[0007] The total exposure period is shortened by the overlap in time ofthe first and second periods. This suppresses blurring in a picturetaken of a subject moving at high speed. Also, the dynamic range isenlarged by generating a still image signal of one screen on the basisof the first and second charges produced by exposures different inperiod.

[0008] In one example of the invention, a first applier applies a firstcharge read pulse to the first light-receiving elements, a secondapplier applies a second charge read pulse to the second light-receivingelements, and a third applier applies a charge sweep-out pulse to thefirst light-receiving elements and the second light-receiving elements.Meanwhile, a shutter member mechanically cuts off incident light on thelight-receiving surface. At this time, the first exposer controls anytwo of the first applier, the third applier and the shutter member tocarry out the first exposure while the second exposer controls any twoof the second applier, the third applier and the shutter member to carryout the second exposure. Due to this, the first period can be madeshorter than the second period, and the first and second periods can beoverlapped in time.

[0009] In one preferred example, the first exposer controls start andend time points of the first exposure by the third and first appliersand the second exposer controls start and end time points of the secondexposure by the third applier and the shutter member.

[0010] In another preferred example, the first exposer controls startand end time points of the first exposure by the first applier and theshutter member and the second exposer controls start and end time pointsof the second exposure by the third applier and the shutter member.

[0011] In another example of the invention, a color filter arranged witha plurality of color elements covers the light-receiving surface. Inthis case, the colors are assigned to both the first light-receivingelements and the second light-receiving elements. Accordingly, the firstcharges caused by each first light-receiving elements correspond to allthe color components of the color filter while the second charges causedby each first light-receiving elements correspond to all the colorcomponents of the color filter

[0012] Preferably the color filter comprises a plurality of color blocksincluding each of the colors, the first and second light-receivingelements being alternately arranged, in a predetermined number in each,in at least one of the vertical and horizontal directions. Furthermore,each of the color elements individually correspond to each of the firstand second light-receiving elements, and the predetermined number iscoincident with the number of color elements of the color block in adirection the first and second light-receiving elements are alternatelyarranged.

[0013] That is, where the first and second light-receiving elements arealternately arranged in the vertical direction, the predetermined numberis the number of color elements of a color block in the verticaldirection. Where the first and second light-receiving elements arealternately arranged in the horizontal direction, the predeterminednumber is the number of color elements of a color block in thehorizontal direction.

[0014] In another example of the invention, the image sensor is aninterline-transfer schemed CCD imager formed with a plurality ofvertical transfer registers in the light-receiving surface.

[0015] The above described objects and other objects, features, aspectsand advantages of the present invention will become more apparent fromthe following detailed description of the present invention when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram showing an embodiment of this invention;

[0017]FIG. 2 is an illustrative view showing a complementary colorfilter applied to the FIG. 1 embodiment;

[0018]FIG. 3 is an illustrative view showing a CCD imager applied to theFIG. 1 embodiment;

[0019]FIG. 4 is magnifying view of a part of the CCD imager shown inFIG. 3;

[0020]FIG. 5 is a magnifying view of another part of the CCD imagershown in FIG. 3;

[0021]FIG. 6 is a block diagram showing a TG applied to the FIG. 1embodiment;

[0022]FIG. 7 is a timing chart showing a part of operation of the FIG. 1embodiment;

[0023]FIG. 8 is a timing chart showing the operation in period A shownin FIG. 7;

[0024]FIG. 9 is a timing chart showing the operation in period B shownin FIG. 7;

[0025]FIG. 10 is a flowchart showing an operation of a CPU applied tothe FIG. 1 embodiment;

[0026]FIG. 11 is a flowchart showing an operation of the TG applied tothe FIG. 1 embodiment;

[0027]FIG. 12 is a timing chart showing a part of operation in anotherembodiment of this invention;

[0028]FIG. 13 is a timing chart showing the operation in period C shownin FIG. 12;

[0029]FIG. 14 is a flowchart showing an operation of the CPU applied tothe FIG. 12 embodiment; and

[0030]FIG. 15 is a flowchart showing an operation of the TG applied tothe FIG. 12 embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Referring to FIG. 1, a digital camera 10 of this embodimentincludes an optical lens 12, a mechanical shutter 14 and a complementarycolor filter 16. The optical image of a subject is passed through thesemembers and illuminated in a vertically inverted state onto alight-receiving surface of a CCD imager 18.

[0032] When displaying a real-time moving image (through-image) on adisplay 34, a timing generator (TG) 26 carries out pre-exposure at atime interval of one frame and reads the pixel signals (charges)produced by each of pre-exposure in a thin-out scheme out of the CCDimager 18. The read pixel signals are subjected to well-known noiseremoval and level adjustment by a CDS/AGC circuit 20. An A/D converter22 converts the pixel signals thus processed into a digital signal. Aswitch SW1 is connected to a side of a signal processing circuit 32 sothat the pixel signal outputted from the A/D converter 22 can beinputted to the signal processing circuit 32 without requiring acombining process by an image combining circuit 24. The signalprocessing circuit 32 performs a predetermined signal process on theinput pixel signal to generate a YUV signal and supplies a generated YUVsignal to a display 34. As a result, a through-image is displayed on thedisplay 34.

[0033] When a shutter button 30 is pressed, a CPU 28 instructs the TG 26to read out all the pixels (or thin-out reading). Thereupon, the TG 26again carries out pre-exposure and reads out the image signal obtainedby the pre-exposure by an interlace scan scheme (or by thin-out readingmentioned above). The read pixel signal is supplied to the signalprocessing circuit 32 in the similar manner to the above. At this time,the signal processing circuit 32 converts the supplied pixel signal intoa YUV signal and integrates the Y component contained in the convertedYUV signal over one-frame period. The CPU 28 fetches an integrationvalue (luminance evaluation value) from the signal processing circuit 32and calculates an exposure time on the basis of the fetched luminanceevaluation value. Note that two exposure time periods (first exposuretime period and second exposure time period) are determined in order toextend the dynamic range. Determining a first exposure period and secondexposure period, the CPU 28 controls the TG 26 and mechanical shutter 14to carry out main exposure totally twice according to a first exposureperiod and second exposure period.

[0034] From the CCD imager 18, outputted first is the charge produceddue to the main exposure in the first exposure period (first exposurepixel signal) and then the charge produced due to the main exposure inthe second exposure period (second exposure pixel signal). Both thefirst exposure pixel signal and the second exposure pixel signal areconverted into digital signals by the A/D converter 22 through noiseremoval and level adjustment by the CDS/AGC circuit 20. The switch SW1at a start of the main exposure is connected toward the image combiningcircuit 24 so that the first and second exposure pixel signals outputtedfrom the A/D converter 22 are inputted to the image combining circuit24. The image combining circuit 24 makes a combining process on thefirst and second exposure pixel signals to generate a combined pixelsignal (still image signal) extended in the dynamic range.

[0035] The signal processing circuit 32 makes a signal process on thecombined pixel signal similarly to that upon outputting through-images,thereby generating a YUV signal to be outputted onto the display 34. Onthe display 34, a subject image (freeze image) due to main exposure isdisplayed. The signal processing circuit 32 furthermore makes JPEGcompression on the YUV signal generated in the above signal process inresponse to a process instruction given from the CPU 28. Then, thecompressed YUV signal produced by the JPEG compression is recorded to arecording medium 36.

[0036] The complementary color filter 16 includes color elements of Ye,Cy, Mg and G, as shown in FIG. 2. The complementary color filter 16, asviewed in a horizontal direction, has Ye and Cy color elementsalternately arranged on the odd line and G and Mg color elementsalternately arranged on the even line. Also, the complementary colorfilter 16, as viewed in the vertical direction, has G and Ye arrangedalternately on the odd row and Mg and Cy alternately arranged on theeven row. That is, the complementary color filter 16 includes aplurality of matrixes (color blocks) each comprising horizontally twopixels and vertically two pixels.

[0037] Referring to FIG. 3, the CCD imager 18 is aninterline-transfer-schemed image sensor. A plurality of light-receivingelements (pixels) 18 a are formed on the light-receiving surface, whichcorrespond one-to-one to a plurality of color elements of thecomplementary color filter 16. On the light-receiving element 18 a, acharge corresponding to any one of color components Ye, Cy, Mg and G isproduced by photoelectric conversion. The produced charge is read onto avertical transfer register 18 b and thereafter transferred in a verticaldirection. Transferred to an end of the vertical transfer register 18 b,the charge is then horizontally transferred by a horizontal transferregister 18 c and outputted out of the CCD imager 18. The read andtransfer processes of the charge are carried out in response to a drivepulse outputted from the TG 26.

[0038] As shown in FIG. 4, the vertical transfer register 18 b is formedwith a plurality of metals M_(v), and each light-receiving element 18 ais assigned with two metals M_(v). To each metal M_(v) is applied anyone of drive pulses V1A, V1B, V2, V3A, V3B and V4 outputted from the TG26. If vertically successive four pixels are considered, the metal M_(v)assigned to the G/Mg pixel of the first line from the bottom is appliedby drive pulses V1A and V2. The metal M_(v) assigned to the Ye/Cy pixelof the second line from the bottom is applied by drive pulses V3A andV4. Also, the metal M_(v) assigned to the G/Mg pixel of the third linefrom the bottom is applied by drive pulses V1B and V2, while the metalM_(v) assigned to the Ye/Cy pixel of the fourth line is applied by drivepulses V3B and V4. If the pixels forming each vertical row areconsidered as sets of four pixels, the drive pulses V1A, V1B, V2, V3A,V3B and V4 are supplied to each of the four pixels in the above manner.

[0039] As shown in FIG. 5, the vertical transfer register 18 c is alsoformed by a plurality of metals M_(H). It is however noted that onemetal M_(H) is assigned to the row on which the vertical transferregister 18 b is provided and one metal to the row on which thelight-receiving element 18 a is provided. A drive pulse H1 is applied tothe metal M_(H) on the row having vertical transfer register 18 b whilea drive pulse H2 is to the metal M_(H) on the row having thelight-receiving element 18 a.

[0040] The TG 26 is concretely configured as shown in FIG. 6. An Hcounter 26 a has a count value (horizontal count value) to beincremented in response to a pixel clock and reset responsive to avertical synchronizing signal. On the other hand, a V counter 26 b has acount value (vertical count value) to be incremented in response to ahorizontal synchronizing signal and reset responsive to a verticalsynchronizing signal. The horizontal count value and the vertical countvalue are both supplied to decoders 26 c 26 n.

[0041] The decoders 2 c and 26 d respectively generate drive pulses H1and H2 on the basis of a horizontal count value and a vertical countvalue. The decoder 26 e generates a timing pulse XSUB on the basis of ahorizontal count value and vertical count value. The driver 26 pgenerates a charge sweep-out pulse VSUB on the basis of a timing pulseXSUB from the decoder 26 e and exposure period data from the CPU 28.

[0042] The decoder 26 f- 26 h respectively generate timing pulses XV1,XSG1A and XSG1B on the basis of the horizontal count value and verticalcount value. The driver 26 q generates drive pulses V1A and V1B on thebasis of the timing pulses XV1, XSG1A and XSG1B from the decoders 26 f-26 h. The decoder 26 i generates a timing pulse XV2 on the basis of thehorizontal count value and vertical count value, while the driver 26 rgenerates a drive pulse V2 on the basis of a timing pulse XV2 from thedecoder 26 i.

[0043] The decoders 26 j- 26 m respectively generate timing pulses XB3,XSG3A and XSG3B on the basis of a horizontal count value and verticalcount value. The driver 26 s generates drive pulses V3A and V3B on thebasis of the timing pulses XV3, XSG3A and XSG3B from the decoders 26 j-26 m. The decoder 26 n generates a timing pulse XV4 on the basis of ahorizontal count value and vertical count value, while the driver 26 tgenerates a drive pulse V4 on the basis of a timing pulse XV4 from thedecoder 26 n.

[0044] When the shutter button 30 is operated, the charge sweep-outpulse Vsub, the drive pulses V1A, V3A, V1B and V3B vary in timing asshown in FIG. 7. First, a charge sweep-out pulse Vsub is outputtedcontinuously. All the charge produced in each light-receiving element 18a is swept away in response to a charge sweep-out pulse Vsub. Firstexposure and second exposure are started simultaneous with thesuspension of outputting the charge sweep-out pulse Vsub. Elapsing afirst exposure period, components XSG1A and XSG3A are respectivelysuperposed over the drive pulses V1A and V3A. This reads, onto thevertical transfer register 18 b, the charge stored on thelight-receiving elements 18 a on the first and second lines shown inFIG. 4. The first exposure period completes with this reading out. Theread charge (first exposure charge) is vertically transferred by thedrive pulses V1A, V1B, V2, V3A, V3B and V4 and thereafter outputtedthrough the horizontal transfer register 18 c.

[0045] The mechanical shutter 14 changes from an open to close state inthe course of vertically and horizontally transferring the firstexposure charge, thereby ending the second exposure period. The chargebuilt up on the light-receiving element 18 a of the third and fourthlines due to the second exposure (second exposure charge) is read ontothe vertical transfer register 18B by the component XSG1B superposed onthe drive pulse V1B and the component XSG3B on the drive pulse V3B. Theread second exposure charge is vertically transferred by the drivepulses V1A, V1B, V2, V3A, V3B and V4 and thereafter outputted throughthe horizontal transfer register 18 c. Herein, the components XSG1B andXSG3B are outputted after completing the output of the first exposurecharge, and accordingly the first and second exposure charges will notbe mixed with each other over the vertical transfer register 18 b orhorizontal transfer register 18 c.

[0046] Referring to FIG. 8, explanation is concretely made on theoperation at around outputting the components XSG1A and XSG3A (periodA). In period t1, the drive pulses V1A, V1B and V2 assume a zero level,and the drive pulses V3A, V3B and V4 a minus level. In period t2, thedrive pulse V4 changes from the minus level to a zero level. In periodt3, the drive pulse V1A changes from the zero level to plus level. Bychanging the drive pulse V1A into the plus level, charge is read out ofthe G/Mg pixel of the first line. The read charge is built up on the twometals M_(v)assigned to the G/Mg pixel of the first line (V1A and V2 areapplied) and one metal MV assigned to the Ye/Cy pixel of the second line(V4 is applied).

[0047] In period t4, the drive pulse V1A returns from the plus level tozero level. In period t5, the drive pulse V4 returns to the zero levelto minus level. By changing the drive pulse V4 from the zero to minuslevel, the charge read in the period t3 is built up on the two metalsM_(v) corresponding to the G/Mg pixel of the first line. In period t6,the drive pulses V1A and V1B change to minus level and the drive pulsesV3A and V3B changes from the minus level to zero level. At this time, itis the drive pulses V2, V3A and V3B that assume zero level, wherein thecharge is built up on the other metal M_(v)assigned to the Ye/Cy pixelof the fourth line (V3B is applied) and one metal M_(v) assigned to theG/Mg pixel of the first line (V2 is applied). In period t7, the drivepulse V4 changes from the minus level to zero level. This builds up thecharge also on the one metal M_(v) assigned to the Ye/Cy pixel of thefourth line (V4 is applied).

[0048] In period t8, the drive pulse V3A changes from the zero level toplus level thereby reading charge out of the Ye/Cy pixel of the secondline. The read charge is built up on the two metals M_(v) assigned tothe Ye/Cy pixel of the second line (V3 and V4 are applied) and one metalM_(v) assigned to the G/Mg pixel of the third line (V2 is applied). Inperiod t9, the drive pulse V3A returns from the plus level to zerolevel. In period t10, the drive pulse V2 changes from the zero level tominus level. By changing the drive pulse V2 to the minus level, thecharge is built up on the two metals assigned to the Ye/Cy pixel of thefourth line (V3A or V3B and V4 are applied).

[0049] In period t11, the drive pulses V1A and V1B change from the minuslevel to zero level and the drive pulses V3A and V3B return from thezero level to minus level. Due to this, the charge is built up on theother metal M_(v) assigned to the G/Mg pixel of the third line (V1A orV1B is applied) and one metal M_(v) assigned to the Ye/Cy pixel of thefourth line (V4 is applied). In period t12, the drive pulse V2 changesfrom the minus level to zero level and the drive pulse V4 changes fromthe zero level to minus level. At this time, the charge is built up onthe two metal M_(v) assigned to the G/Mg pixel of the first and thirdline (V1A or V1B and V2 are applied).

[0050] The charge produced due to the first exposure is thus read fromthe G/Mg pixel of the first line and Ye/Cy pixel of the second line ontothe vertical transfer register 18 b, and vertically transferred withoutbeing mixed with each other. Incidentally, no charge is read out of theG/Mg pixel of the third line and Ye/Cy pixel of the fourth line, andcharge accumulation due to the second exposure is continued.

[0051] Referring to FIG. 9, explanation is made on the concreteoperation at around the output of the components XSG1B and XSG3B (periodB). In period t1, the drive pulses V1A, V1B and V2 assume a zero leveland the drive pulses V3A, V3B and V4 a minus level. In period t2, thedrive pulse V4 changes from a minus level to zero level. In period t3,the drive pulse V1B changes from the zero level to plus level. Thecharge stored on the G/Mg pixel of the third line is read out in periodt3. The read charge is built up on the two metals M_(v) assigned to theG/Mg pixel of the third line (V1B and V2 are applied) and one metal M_(v) assigned to the Ye/Cy pixel of the fourth line (V4 is applied).

[0052] In period t4, the drive pulse V1B returns from the plus level tozero level. In period t5, the drive pulse V4 returns from the zero levelto minus level. By changing the drive pulse V4 from the zero level tominus level, the charge read in the period t3 is built up on the twometals M_(v) corresponding to the G/Mg pixel of the third line. Inperiod t6, the drive pulses V1A and V1B change to minus level and thedrive pulses V3A and V3B change from the minus level to zero level. Atthis time, the charge is built up on the other metal M_(v) assigned tothe Ye/Cy pixel of the second line (V3A is applied) and one metal M_(v)assigned to the G/Mg pixel of the third line (V2 is applied). In periodt7, the drive pulse V4 changes from the minus level to zero level,thereby accumulating charge also to the one metal M_(v) assigned to theYe/Cy pixel of the second line (V4 is applied).

[0053] In period t8, the drive pulse V3 changes from the zero level toplus level thereby reading charge from the Ye/Cy pixel of the fourthline. The read charge is built up on the two metals M_(v) assigned tothe Ye/Cy pixel of the fourth line (V3B and V4 are applied) and the onemetal M_(v) assigned to the G/Mg pixel of the first line (V2 isapplied). In period t9, the drive pulse V3B returns from the plus levelto zero level. In period t10, the drive pulse V2 changes from the zerolevel to minus level. The charge is stored to the two metals M_(v)assigned to the Ye/Cy pixel of the fourth line (V3A or V3B and V4 areapplied).

[0054] In period t11, the drive pulses V1A and V1B return from the minuslevel to zero level and the drive pulses V3A and V3B return from thezero level to minus level. Due to this, the charge is built up on theother metal M_(v) assigned to the G/Mg pixel of the third line (V1A orV1B is applied) and the one metal M_(v) assigned to the Ye/Cy pixel ofthe fourth line (V4 is applied). In period t12, the drive pulse V2changes from the minus level to zero level and the drive pulse V4changes from the zero level to minus level. At this time, the charge isbuilt up on the two metals M_(v) assigned to the G/Mg pixel of the thirdline V1A or V1B and V2 are applied.

[0055] The charge produced by the second exposure is thus read from theG/Mg pixel of the third line and Ye/Cy pixel of the fourth line onto thevertical transfer register 18 b and then transferred separately in thevertical direction.

[0056] The CPU 28 concretely operates according to a flowchart shown inFIG. 10. When the power is on, first in step S1 the switch SW1 isconnected toward the signal processing circuit 32. Next, it isdetermined in step S3 whether the shutter button 30 has been pressed ornot. If “NO”, the process proceeds to step S5 to make display process ofa through image. That is, the TG is instructed to carry out thin-outreading and the signal processing circuit 32 is given a process command.Due to this, part of the pixel signal is outputted from the CCD imager12. The output pixel signal is inputted to the signal processing circuit32 through the CDS/AGC circuit 20, A/D converter 22 and switch SW1. Thesignal processing circuit 32 converts the input pixel signal into a YUVsignal and outputs a converted YUV signal onto the display 34. Thisprovides display of a through-image.

[0057] When the shutter button 30 is pressed, determination of “YES” ismade in step S3. In step S7, the TG 26 is instructed to carry outpre-exposure and all-pixel read out. In step S9, a luminance evaluationvalue based on the pixel signal generated by the pre-exposure in thestep S7 is fetched from the signal processing circuit 32. In thesucceeding step S11 first and second exposure time periods arecalculated on the basis of the fetched luminance evaluation value.Completing the process in the step S11, in step S13 the switch SW1 isconnected to the image combining circuit 24. In step S15, the TG 26 isinstructed to carry out main exposure and the mechanical shutter 14 isclosed in predetermined timing. This outputs first and second exposurepixel signals out of the CCD imager 18, and the output pixel signals arecombined together by the image combining circuit 24. In step S17, thesignal processing circuit 32 is supplied with a record processingcommand. The combined pixel signal outputted from the image combiningcircuit 24 is converted into a YUV signal in the signal processingcircuit 32 and subjected to JPEG compression. The compressed YUV signalis recorded in a recording medium 36. During a record process, the YUVsignal based on the combined pixel signal is outputted also to thedisplay 34 thereby displaying a freeze image. Completing the recordprocess, in step S19 the mechanical shutter 14 is opened and then theprocess returns to step S1.

[0058] The TG 26 when instructed for main exposure in step S15 operatesaccording to a flowchart shown in FIG. 11. Note that this flowchart isfor the explanation sake because the TG 26 is configured by hardware asdescribed before. Also, at the time point of instructing the mainexposure, the drive pulses H1 and H2 for horizontal transfer and thedrive pulses V1A, V1B, V2, V3A, V3B and V4 for vertical transfer havealready been outputted. A charge sweep-out pulse Vsub has been outputtedin response to the vertical synchronizing signal.

[0059] First, the driver 26 p determines in step S21 whether in timingfor starting exposure on the basis of exposure-time data. Whenexposure-start timing comes, in step S23 the charge sweep-out pulse Vsubis suspended from outputting. This starts first exposure and secondexposure. The decoders 26 g and 26 k in step S25 determines whether afirst exposure period has elapsed or not. When a first exposure periodhas elapsed, in step S27 timing pulses XSG1A and XSG3A are outputted.The timing pulse XSG1A is superposed over the drive pulse V1A by thedriver 29, while the timing pulse XSG3A is over the drive pulse V3A bythe driver 26 s. This reads charge (first exposure charge) from G/Mgpixel of the first line and Ye/Cy pixel of the second line, thus endingthe first exposure. The read charge is passed through the verticaltransfer register 18 b and horizontal transfer register 18c and thenoutputted from the CCD imager 18.

[0060] After the process of step S27, the mechanical shutter 14 isclosed in predetermined timing thereby ending the second exposure. Thedecoders 26 h and 26 m in step S29 determines whether the first exposurecharge has been outputted or not. If having been outputted, in step S31timing pulses XSG1B and XSG3B are outputted. The timing pulse XSG1B issuperposed over the drive pulse V1B by the driver 26 q while the timingpulse XSG3B is over the drive pulse V3B by the driver 26 s. This readscharge (second exposure charge) from the G/Mg pixel of the third lineand Ye/Cy pixel of the fourth line. If the second exposure charge hasbeen outputted, “YES” is determined in step S33 thus ending the mainexposure process.

[0061] According to this embodiment, first exposure and second exposureare simultaneously started by the suspension of outputting the chargesweep-out pulse Vsub. Also, the first exposure is ended by reading outthe first exposure charge and the second exposure is ended by closingthe mechanical shutter. This reduces the first exposure period shorterthan the second exposure period, and overlaps in time the first exposureperiod with the second exposure period. Accordingly, by combining thefirst exposure charge (first exposure pixel signal) and the secondexposure charge (second exposure pixel signal) in the image combiningcircuit, a combined image signal (still image signal) can be producedwith enlarged dynamic range but less in blurring.

[0062] Meanwhile, in this embodiment, the image sensor at itslight-receiving surface is covered with a complementary color filterarranged with color elements of Ye, Cy, Mg and G. Herein, the colorelements G and Mg are assigned to the first and third lines while thecolor elements Ye and Cy are to the second and fourth lines. That is,the color elements Ye, Cy, Mg and G are assigned to both thelight-receiving element subjected to first exposure (firstlight-receiving element) and the light-receiving element subjected tosecond exposure (second light-receiving element). Furthermore, the firstlight-receiving elements and the second light-receiving elements arealternately arranged two per each (coincident with the number of colorelements of a color block in the vertical direction) in the verticaldirection. Due to this, the first exposure pixel signal and the secondexposure pixel signal each contain color components, Ye, Cy, Mg and G.Moreover, there is no great deviation between an image to be formed bythe first exposure pixel signal and an image to be formed by the secondexposure pixel signal.

[0063] A digital camera 10 of another embodiment is configured likewisethe foregoing (as shown in FIG. 1 to FIG. 5) and hence duplicatedexplanation on the configuration will be omitted. The difference lies inthe operation of the TG 26 and process of CPU 26 when making firstexposure and second exposure to the CCD imager 18.

[0064] When the shutter button 30 is operated, the charge sweep-outpulse Vsub and the drive pulses V1A, V3A, V1B and V3B vary in timing asshown in FIG. 12. First, the charge sweep-out pulse Vsub is continuouslyoutputted so that all the charge caused on the light-receiving elements18 a is swept away by the charge sweep-out pulse Vsub. When the chargesweep-out pulse Vsub is suspended from outputting, a second exposureperiod is started. After elapsing a predetermined time period from thestart of the second exposure, the charge built up on the light-receivingelement 18 a on the first and second lines is read onto the verticaltransfer register 18 b by the component XSG1A superposed on the drivepulse V1A and component XSG3A on the drive pulse V3A. The charge readout herein is unwanted charge and the first exposure period is startedupon reading the charge.

[0065] After elapsing a predetermined period from the start of the firstexposure, the mechanical shutter 14 changes from an open to close statethereby ending both the first exposure and second exposure. After endingthe first exposure and second exposure, the vertical transfer register18 b and the horizontal transfer register 18 c are reset by the CPU 28in order to exclude unwanted charge containing smear components.Elapsing a predetermined reset period, the charge built up on thelight-receiving element 18 a on the third and fourth lines (secondexposure charge) is read onto the vertical transfer register 18 b by thecomponent XSG1B superposed on the drive pulse V1B and component XSG3B onthe drive pulse V3B. The read second exposure charge is verticallytransferred by the drive pulses V1B and V3B and thereafter outputtedthrough the horizontal transfer register 18 c.

[0066] After completing the reading of the second exposure charge, thevertical transfer register 18 b and the horizontal register 18 c areagain reset by the CPU 28. After elapsing a predetermined reset period,outputted are a drive pulse VIA superposed with the component XSG1A anda drive pulse V1B with the component XSG3A. This reads the charge builtup on the first exposure period to the vertical transfer register 18 bfrom the light-receiving elements 18 a of the first and second lines.The read first exposure charge is outputted through the horizontaltransfer register 18 c. In the second round of the period of outputtingthe components XSG1A and XSG3A (period A) and the period of outputtingthe components XSG1B and XSG3B (period B), the drive pulses V1A, V1B,V2, V3A, V3B and V4 vary as shown in FIG. 8 and FIG. 9. On the otherhand, in the first round of the period of outputting the componentsXSG1A and XSG3A (period C), the drive pulses V1A, V1B, V2, V3A, V3B andV4 vary as shown in FIG. 13.

[0067] Referring to FIG. 13, in period t1 the drive pulses V1A, V1B, V2and V3A assume a zero level and the drive pulses V3B and V4 a minuslevel. In period t2, the drive pulse V3B changes from the minus level tozero level. In period t3, the drive pulses V1A and V3 change from thezero level to plus level. This reads out the charge built up on the G/Mgpixel of the first line and Ye/Cy pixel of the second line. The chargeread from the G/Mg pixel of the first line is stored in the two metalsM_(v) assigned to the same G/Mg pixel (V1A and V2 are applied and onemetal M_(v) assigned to the Ye/Cy pixel of the fourth line (V3B isapplied). The charge read from the Ye/Cy pixel of the second line isbuilt up on the other metal M_(v) assigned to the same Ye/Cy pixel (V3Ais applied) and the two metals M_(v) assigned to the G/Mg pixel of thethird line (V1B and V2 are applied).

[0068] In this manner, the charge read to the vertical transfer register18 b will be vertically transferred in period of t4 or the later. Notethat this charge is unwanted charge and meaningless in the later-stagedsignal process.

[0069] The CPU 28 concretely processes a flowchart shown in FIG. 14.Note that the steps S41-S53 and steps S57 and S59 in this flowchart isthe same as that the steps S1-S13 and S17 and S19 shown in FIG. 10 andhence duplicated explanation will be omitted. In step S55, the TG 26 isinstructed for main exposure. The mechanical shutter 16 is closed intiming of ending the first exposure and second exposure, and thevertical transfer register 18 b and the horizontal transfer register 18c are reset in a predetermined period after ending the first and secondexposure and in a predetermined period after ending the reading out ofthe second exposure charge.

[0070] TG 26 operates according to a flowchart shown in FIG. 15. In stepS61, the driver 26 p determines based on the exposure time data from theCPU 28 whether it is in second exposure start timing or not. When secondexposure start timing comes, the driver 26 p in step S63 suspends thecharge sweep-out pulse Vsub from outputting. The decoders 26 g and 26 kdetermine in step S65 whether it is in first exposure start timing ornot. When determined “YES”, in step S67 timing pulses XSG1A and XSG3Aare outputted. This reads the unwanted charge from the G/M pixel of thefirst line and Ye/Cy pixel of the second line. From then on, firstexposure is started.

[0071] Elapsing a predetermined period from starting the first exposure,the CPU 28 closes the mechanical shutter 14 and resets the verticaltransfer register 18 b and horizontal transfer register 18 c. Theclosure of the mechanical shutter 14 simultaneously completes the firstexposure and the second exposure. Thus, the unwanted charge is excludedby resetting the vertical transfer register 18 b and horizontal transferregister 18 c .

[0072] After elapsing a predetermined reset period, the decoders 26 hand 26 m in step S69 outputs timing pulses XSG1B and XSG3B. This readscharges (second exposure charge) out of the G/Mg pixel of the third lineand Ye/Cy pixel of the fourth line. The read second exposure charge isoutputted through the vertical transfer register 18 b and horizontaltransfer register 18 c. The CPU 28 resets the vertical transfer register18 b and horizontal transfer register 18 c in the timing completing theoutput of the second exposure charge and excludes the second exposurecharge remaining on the registers 18 b and 18 c. Step S71 is executed inthe timing the predetermined reset period. In this step, the decoders 26g and 26 k output timing pulses XSG1A and XSG3A, thereby reading thefirst exposure charge out of the G/Mg pixel of the first line and Ye/Cypixel of the second line. The read first exposure charge is outputtedthrough the vertical transfer register 18 b and horizontal transferregister 18 c. Completing the output of the first exposure charge, instep S73 determination of “YES” is made, thus ending the main exposure.

[0073] According to this embodiment, second exposure is started bysuspending the charge sweep-out pulse Vsub from outputting while firstexposure is started by reading out unwanted charge. Also, the closure ofthe mechanical shutter ends the first exposure and second exposuresimultaneously. Due to this, the first exposure period is made shorterthan the second exposure period, and the first exposure period and thesecond exposure period overlap in time. Accordingly, by combining thefirst exposure charge (first exposure pixel signal) and the secondexposure charge (second exposure pixel signal) are combined in the imagecombining circuit, a combined pixel signal (still image signal) can beproduced with enlarged dynamic range and less blurring.

[0074] Meanwhile, in this embodiment, the light-receiving surface of theimage sensor is covered with a complementary color filter arranged withcolor elements Ye/Cy, Mg and G. All the colors Ye, Cy, Mg and G areassigned to the light-receiving elements to be subjected to firstexposure (first light-receiving element) and light-receiving elements tobe subjected to second exposure (second light-receiving element). Also,the first light-receiving elements and the second light-receivingelements are alternately arranged to in each in the vertical direction(coincident with the number of color elements of a color block in thevertical direction). Accordingly, the first exposure pixel signal andthe second exposure pixel signal both include color components Ye, Cy,Mg and G, wherein there is no possibility of causing great deviation inlevel between the first exposure period signal and the second exposurepixel signal.

[0075] Incidentally, although the above two embodiments are attachedwith the complementary color filter on the light-receiving surface ofthe image sensor, a primary color filter may be of course used in placeof the complementary color filter. Also, although the above twoembodiments use the CCD-type image sensor, this invention can use aCMOS-type image sensor. Furthermore, although the CCD imager used inabove two embodiments is an interlace-scan CCD imager, aprogressive-scan (three or more metals are assigned to eachlight-receiving element) CCD imager may be used. Furthermore, althoughthe above two embodiments had the first light-receiving elements and thesecond light-receiving elements arranged alternately, two in each (thevertical number of color elements in a color block) in the verticaldirection, the first and second light-receiving elements may bealternately arranged, two in each, in the horizontal direction. Also,they may be arranged, two in each, in the both vertical and horizontaldirections, i.e. in a mosaic form.

[0076] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

What is claimed is:
 1. A digital camera, comprising: an image sensorformed, in a light-receiving surface, with a plurality of firstlight-receiving elements and a plurality of second light-receivingelements; a first exposer for subjecting said first light-receivingelements to first exposure for a first period; a second exposer forsubjecting said second light-receiving elements to second exposure for asecond period; an outputter for separately outputting, from said imagesensor, a first charge produced in said first light-receiving elementsdue to the first exposure and a second charge produced in said secondlight-receiving elements due to the second exposure; and a generator forgenerating a still image signal of one screen on the basis of said firstcharge and said second charge; wherein said first period is shorter thansaid second period and overlapped in time with said second period.
 2. Adigital camera according to claim 1 , further comprising a first applierto apply a first charge read pulse to said first light-receivingelements, a second applier to apply a second charge read pulse to saidsecond light-receiving elements, a third applier to apply a chargesweep-out pulse to said first light-receiving elements and said secondlight-receiving elements, and a shutter member to mechanically cut offincident light on said light-receiving surface, wherein said firstexposer controls any two of said first applier, said third applier andsaid shutter member to carry out the first exposure while said secondexposer controls any two of said second applier, said third applier andsaid shutter member to carry out the second exposure.
 3. A digitalcamera according to claim 2 , wherein said first exposer controls startand end time points of the first exposure by said third and firstappliers and said second exposer controls start and end time points ofthe second exposure by said third applier and said shutter member.
 4. Adigital camera according to claim 2 , wherein said first exposercontrols start and end time points of the first exposure by said firstapplier and said shutter member and said second exposer controls startand end time points of the second exposure by said third applier andsaid shutter member.
 5. A digital camera according to claim 1 , furthercomprising a color filter arranged with a plurality of color elementscovering said light-receiving surface, wherein the colors are assignedto both the first light-receiving elements and said secondlight-receiving elements.
 6. A digital camera according to claim 5 ,wherein said color filter comprises a plurality of color blocksincluding each of the colors, said first and second light-receivingelements being alternately arranged, in a predetermined number in each,in at least one of the vertical and horizontal directions, each of thecolor elements individually corresponding to each of said first andsecond light-receiving elements, and the predetermined number beingcoincident with the number of color elements of the color block in adirection said first and second light-receiving elements are alternatelyarranged.
 7. A digital camera according to claim 1 , wherein said imagesensor is an interline-transfer schemed CCD imager formed with aplurality of vertical transfer registers in said light-receivingsurface.